The invention relates to a method of forming three-dimensional envelopes from blanks.
Usually, sewn three-dimensional envelopes are manufactured by laying flat the blanks to be sewn together in a sewing machine and by passing them under the sewing foot of the sewing machine. The edges of the blanks are provided with marks which have to be placed matchingly one upon the other. This kind of sewing requires a high degree of skill. Nevertheless, it cannot be avoided that the blanks are displaced relative to each other during sewing which results in wave formations and gatherings in the envelope during manufacture.
The performance facilities of the sewing machine are not utilized owing to the relatively slow manual control.
From DE 33 38 405 A1, a method for manufacturing three-dimensional envelopes of articles provided with sewn seams is known, wherein blanks are fastened to a three-dimensional carrier body and a sewing machine fastened to a manipulator arm is moved along the intended seam line. The edges of the blanks are laid flat, one upon the other, on the carrier body, and the needle of the sewing machine is pierced through the edges into the carrier body. This requires the introduction of a rotating gripper into the interior of the carrier body for producing the seam.
In another method known from EP 0 344 400 A1 for sewing an arm sleeve into a jacket, the sleeve is inserted into the reversed jacket such that the edge of the sleeve opening is laid from the inside against the edge of the jacket opening (armhole). For sewing, a sewing machine is led around the edges lying together, the needle plate with the rotating gripper arranged beneath being introduced into the opening. A problem that arises is that the outer edge and the inner edge which is enclosed by the outer one have different diameters during the sewing process so that these edges, one lying within the other, are subject to forces.